This type of separation plant, treating large gas flow rates with rapid cycle sequences, poses problems regarding circulation and distribution of the gases, which are further exacerbated in plants in which gas flows pass horizontally through the adsorbent, as is the case here. Furthermore, the annular bed is delimited by a lower wall which has to support the weight of the annular volume of particulate material, the forces resulting from the pressure differences on either side of this wall, in particular during the repressurization or depressurization steps in which head losses are created, as well as possibly the forces resulting from the packing means applied to the upper surface of the volume of particulate material.
A gas separation plant of this type is described in document EP-A-0,759,320 in the name of the Applicant Company. In this document, the lower wall, which is plane, has a considerable thickness in order to support the volumes of particulate materials, the space inside the latter as well as the space between the lower wall and the lower domed end of the container including perforated partitions for homogenizing the gas flows in these spaces.
After intensive research, the Applicant Company has observed that the shape of the lower walls of the adsorbent beds had substantial repercussions on proper distribution of the gas flows through the annular volume of particulate materials, and that it could in particular create deficiencies in distribution of gas flows, which are not limited to the adjacent zones but have a not insignificant effect actually within the volumes of particulate materials.
The Applicant Company has thus demonstrated that, in spite of the problems of mechanical strength which this poses, the end walls should not be domed and should be very slightly conical and not have any part forming an angle in excess of 15.degree. with the horizontal. With shapes of this type, in order to achieve the requisite mechanical strength, it is possible, as in the aforementioned document, to provide a thick end wall bearing on the central feed duct. However, further to the problems of excess weight, the use of thick walls accentuates the radial heat transfer, and this modifies the temperature profile of the adjacent zones of the adsorbent beds, which therefore operate under different temperature conditions from those which are developed in the central adiabatic part of these beds, thus preventing optimum operation of the plant from being achieved. It is also envisagable to use radial stiffness under the lower wall, but studies carried out on architectures of this type show that this stiffness substantially modified the flow of the gases in the lower part of the container, creating preferential circulation channels towards the lateral gas passage.